Store Coin annotations in InfluxDB

This task is about Coin writing annotations in the time-series database. This information could include:

• When an integration starts/ends
• When different workitems start/end
• the different stages inside the workitems
• etc (feel free to edit)

This will enable us to

• annotate the graphs in Grafana with human-readable information regarding what happens on our CI hardware
• visualising how much time Coin spends in all the different stages (waiting for hardware, for sources, etc) right after the user presses the "schedule build" button.

daniel.smith is working on instrumenting both the Coin agent and server here:

• https://codereview.qt-project.org/c/qtqa/tqtc-coin-ci/+/273083
• https://codereview.qt-project.org/c/qtqa/tqtc-coin-ci/+/272963